Ribbons of silicon that are useful in applications such as the construction of solar cells, can be constructed by edge supported growth. In such ribbon growth, a pair of filaments pass vertically through holes in the bottom of a container and through a molten bath or melt of silicon in the container. As the filaments are slowly pulled upwardly, silicon is drawn out of the melt to form a ribbon whose edges are defined by the filaments.
A major problem in the use of the edge-supported process for the growth of silicon ribbon, is that it is difficult to find filaments which have substantially the same thermal expansion coefficient as the ribbon of silicon, so as to grow ribbons with little residual stress. A compound that has been developed for use as a substrate in the SOC (silicon on ceramic) process is mullite (3Al.sub.2 O.sub.3.2SiO.sub.2) which has a thermal expansion coefficient substantially the same as that of silicon. Unfortunately, this material can contaminate a silicon melt, as where a filament extends through the height of a typical prior art melt having a height on the order of a centimeter and a temperature of about 1415.degree. C. and the filament is pulled up at a rate such as 2 centimeters per minute. If a system and method could be developed which permitted the use of such a filament material so that it grew a ribbon of silicon but had minimal contact with the silicon melt, then this would facilitate the growing of silicon ribbon that was substantially free of stresses.
Another problem that has arisen in edge-supported silicon ribbon growth, is that the height of the melt has been severely limited, as to a height of about 1 centimeter. If the height of the melt increased greatly beyond this, then there was danger that the weight of the silicon tending to cause it to drip through the filament-holes in the bottom of the container, would exceed the resistance to such leakage by the surface tension of the silicon. It is important that the temperature of the silicon melt be maintained constant, which would be aided if a melt of considerable height could be used. A system and method which permitted a melt of considerable height to be used would also aid in conducting the process of edge-supported silicon ribbon growth.